US 3408625 A
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Description (OCR text may contain errors)
Oct. 29, 1968 K. R. SKINNER 3,408,625 LAMP BURNOUT DETECTION CIRCUIT Filed Aug. 3, 1965 Hm FLASHER IN VEN TOR.
A T TOEZVEI United States Patent Filed Aug. 3, 1965, Ser. No.
4 Claims. (Cl. 340-79 ABSTRACT OF THE DISCLOSURE A circuit for detecting burnout of a turn signal lamp is disclosed which utilizes the usual turn signal pilot lamp as a lamp burnout indicator. The circuit includes a turn signal switch which, in the neutral position, connects a truck or bus. is equipped with a plurality of siglamps such as, for example,
When a vehicle burnout of a signal lamp.
In accordance with the present invention, a lamp burntional turn signal indicating lamp installed within the vehicle.
Referring now to the single figure, a plurality of exteriorly mounted left and right signal lamps are designated and 12 respectively. Matched resistors 14 and 3,408,625 Patented Oct. 29, 1968 Work having input terminals connected across the battery 18 and output terminals minals 20 and 21 respectively.
A flasher shown in block diagram and nated 32 may be of the type shown in plication Ser. No. 346,905
generally desigcopending apassigned to the assignee of 12. With the left turn inthe lamps 10 and light because of the resistors 14 en the turn signal switch electrodes respectively of the transistor 44. If the sig nal lamps and 12 are in satisfactory condition, the voltage at the terminals and 21 will be the same. With equal voltages at the emitter and base electrodes of the transistors 42 and 44, these transistors are non-conductive and thus no collector current flows through the resistors 46. Under this condition the transistor 48 is rendered conductive and energizes the coil 52 to draw the armature 54 to a position connecting the indicator lamp 60 to the flasher 32 through the conductor 64. If the turn signal switch 24 should now be placed in operating position, the signal lamps 10 or 12 and the indicator lamp 60 will be periodically energized. Movement of the contacts 28 and 30 to an operating position disconnects the stationary contacts 26 and 27 from the output terminals 20 and 21. This prevents the detector circuit from giving an erroneous output signal resulting from changes in the voltage at the terminals 20 and 21 which must necessarily occur at one terminal during operation of the flasher 32. It will be apparent, however, with the detector network disconnected from the terminals 20 and 21 the transistor 48 will be conductive thereby maintaining the connection of the indicator lamp to the flasher 32. Accordingly, the indicator lamp 60 performs the conventional function of flashing while the signal lamps 10 or .12 are energized and continues to do so even though one of the signal lamps may have burned out. If, however, a signal lamp has burned out and the turn signal switch 24 is in the neutral position which would normally occur after the turn is completed or during normal straight-ahead driving, a difference in potential will exist at the output terminals 20 and 21. This will render one of the transistors 42 or 44 conductive depending upon whether a lamp has burned out on the left or right side of the vehicle. If, for example, one of the left signal lamps 10 has burned out, the voltage at the terminal 20 will be positive with respect to the voltage at the terminal 21 thus raising the potential of the emitter with respect to the base of transistor 42 and rendering the transistor 42 conductive. The transistor 44 will be cut ofi since its base electrode will be positive with respect to the emitter electrode. If one of the right turn signal lamps 12 is burned out, the opposite condition will prevail. In either case, collector current will flow through the resistor 46 raising the potential at the emitter of transistor 48 causing it to be cut oif thus deenergizing the coil 52 whereupon the armature 54 connects the indicator lamp 60 directly to the battery 18 through the conductor 62. The indicator lamp 60 is thus continuously energized to indicate to the driver that a signal lamp burnout has occurred.
While the invention has been described with regards to a preferred embodiment thereof, this should not be construed in a limiting sense. Numerous modifications and variations will occur to those skilled in the art. For a definition of the invention, reference is made to the appended claims.
I claim: a
1. A lamp burnout indicating circuit comprising a bridge network having an input and an output terminal and including first and second impedance elements connected in series with a first and second plurality of signal lamps respectively,
means for connecting said input terminals to a source of voltage,
detector means for indicating an unbalance in said bridge and including first and second transistors having emitter, base and collector electrodes,
the emitter electrode of each of said transistors being connected to the base electrode of the other transistor with the collector electrodes of each transistor being connected together, the emitter electrode of each of said transistors also being connected respectively to the output terminals of said bridge network whereby at least one of said transistors is rendered conductive when an unbalance exists in said bridge network, a third transistor having emitter,
electrodes, means establishing a reference potential at the base electrode of said third transistor," means establishing a potential at the emitter electrode of said third transistor in accordance .with the output of said detector means, relay means, means for connecting said relay means between said source and the collector electrode of said third transistor, an indicator lamp, sa'id relay means including an armature for connecting said indicator lamp to said source of voltage. 2. In a motor vehicle provided with the source of DC voltage,
a plurality of left and right signal lamps mounted exteriorly of said vehicle, an indicator lamp,
turn signal switching means movable from a neutral position to an operating position for selectively connecting said lamps to said source,
a flasher connected between said source and said lamps when said turn signal switch is in operating position for periodically disconnecting said lamps from said source,
the improvement comprising impedance means connected in series with said left and right signal lamps respectively to form a bridge network having input and output terminals,
base and collector means connecting said source to said input terminals,
detector means having input and output terminals,
said turn signal switch connecting the input terminals of said detector means to the output terminals of said bridge network when said turn signal switch is in a neutral position,
means responsive to the output of said detector means for disconnecting said indicator lamp from the output of said flasher and connecting said indicator lamp in parallel with said flasher.
3. In a motor vehicle having left and right signal lamps mounted exteriorly of said vehicle and an indicator lamp mounted within said vehicle,
a lamp burnout detection circuit comprising a source of D-C voltage,
first and second impedance elements connecting said left and right signal lamps respectively in series with said source.
a turn signal switch movable from a neutral position to an operating position,
said turn signal switch connecting said detector means to the junction between said impedance means and said left and right signal lamps while in said neutral position,
said turn signal switch disconnecting said detector means from said junction and connecting said flasher in parallel with said impedance means while in an op erating position,
relay means responsive to the output of said detector means for selectively connecting said indicator lamp -in series with said flasher or in parallel with said flasher.
4. In a motor vehicle having left and right signal lamps mounted exteriorly of said vehicle and an indicator lamp mounted within said vehicle,
a lamp burnout detection circuit comprising a source of D-C voltage having first and second terminals, first and second resistor means connecting said left and right signal lamps respectively to the first terminal of said source,
the input electrode of each of said transistors being connected to the common electrode of the other transistor with the output electrodes of each transistor being connected together,
said left and right contact means when located in said electrodes of said first and second transistors to the second terminal of said source,
a third transistor having input, output and common electrodes,
References Cited UNITED STATES PATENTS 2,843,802 7/1958 Brohl 3l577 3,345,558 10/1967 Christian 323-75 JOHN W. CALDWELL, Primary Examiner. D. MYER, Assistant Examiner.